Salmonella species cause disease or death in millions of individuals every year who ingest contaminated food or water. Individuals who survive Salmonella infection develop robust immunity that is dependent on antibodies that facilitate bacterial phagocytosis by macrophages, and lymphokines from CD4+ T cells that stimulate macrophages to kill engulfed bacteria. For practical reasons, a subunit vaccine capable of inducing the level of immunity that can be induced by live organisms, is desirable. Unfortunately, immunization with individual Salmonella proteins usually induces only partial immunity. The long-term goal of this project is to overcome this inefficiency and produce an effective subunit vaccine for Salmonella. Our hypothesis is that individual Salmonella proteins are less protective than attenuated organisms because of a lack of presentation at all times during infection, inherently weak adjuvant activity, and poor entry into the mucosal lymphoid organs. Our specific aim is to produce a single vaccine that addresses each of these weaknesses. We propose to identify immunodominant peptides from S. typhimurium proteins that activate CD4+ T cells early and late after S. typhimurium infection. These peptides will be incorporated into particles along with the Toll-like receptor 5-binding portion of S. typhimurium FliC, which functions as an adjuvant and contains B cell epitopes, and the beta 1 integrin-binding domain of Yersinia pseudotuberculosis, which facilitates M cell translocation of particles into the Peyer's patches. The particles containing all of these components will be tested for the ability to generate protective immunity to Salmonella, and novel methods to track peptide:MHC II complexes, specific CD4+ T cells, and antibodies will be employed to assess the cellular mechanisms responsible for immunity. Completion of these aims will provide a framework for the rational design of effective subunit vaccines for Salmonella, other infectious agents, and cancer.